1. Field of the Invention
The present invention relates to a method of making a cylindrical coreless armature for brushless motors and alternating current motors.
2. Description of the Prior Art
As is already known, a brushless motor or alternating current motor, for example, the brushless motor, comprises a magnetic rotor provided with a permanent magnet fixed to the shaft therof and a stator comprising a cylindrical coreless armature which is disposed around the rotor and which is provided on a case in the outside thereof. The coreless armature has a cylindrical shape formed by a plurality of specified turns of coil. The various types of coreless armatures available include one which is formed by a single layer coil and one which is formed by laminating two or more layers of coil. The later type generally generates an increased output from the motor comprising this type of armature.
A prior art example producing this sort of coreless armature is a method in which armature coils are prepared in advance with a cup-like shape by self-welding wires, a necessary amount of solid resin is placed in a mold, the prepared armature coils are placed on the solid resin and covered with another mold so that the armature coils are molded into a desired shape and are fixed by charging the solid resin in the mold under heating (see, for example, Japanese Patent Laid-Open No. 125061/1980).
Another example of prior art is a technique in which an attempt is made to reduce the thickness of an armature by adopting an arrangement in which coils are bent into U-shaped forms and disposed in two layers around a cylinder, one of the two layers having a larger diameter than the other in an overlapping portion (see, for example, Japanese Utility Model Laid-Open No. 75702/1978).
Another type of armature is known which comprises a cylindrical armature winding formed by producing a plurality of winding units and then combining these winding units (see, for example, Japanese Utility Model Publication No. 31176/1981).
A technique concerning a molded stator has also been disclosed in Japanese Utility Model Laid-Open No. 55906/1976 in which an outgoing lead wire for each of the phase coils and an outgoing lead wire for a Hall element, provided for the purpose of detecting the positions of rotor magnetic poles are connected to a printed board which is provided on the surface at one end of a cylindrical stator coil to form an independent structure as a unit. The cylindrical armature disclosed in this publication is formed by inserting a plurality of armature windings which are wound or shaped in advance into a desired shape in a mold, and burying the windings in the heated resin in a semi-solidified state which is charged under pressure through a gate provided at an opening of the mold to be molded into a cylindrical form as a unit. The mold used for forming the bore portion of the cylindrical armature is generally formed as a unit from one end of the armature to the other end thereof, with a draft being provided so that the armature fixed by the resin can be easily separated from the mold. The above-described conventional cylindrical armature therefore has the bore inclined in one direction from one end to the other end thereof which is formed by the draft of the mold.
Coreless multi-layer armatures of the type formed by laminating two or more layers of coil have the problems described below with respect to the production thereof.
1. Although it is desirable that the linear portion of the winding of a coil which functions to generate torque is as large as possible, if this requirement is satisfied, the size of an armature is increased. In this case, even though the thickness of the armature can be reduced by a distributed winding in which conductors are arranged around the circumference of a cylinder without any gaps, antitorque is produced according to the arrangement of the conductor. If a concentrated winding in which conductors are concentrated at portions near the boundary between magnetic poles is employed, even though no antitorque is produced, there is a problem in that the thickness of the armature has to be increased.
2. A process of producing an armature in which coils arranged in a cylindrical form are fixed by molding with resin using a mold has the following problems:
(1) Although fixing of coils is performed by molding in a mold after they have been shaped into a cylindrical form so that they do not loosen, the coils are likely to lose their shape or become damaged when the coils are placed in the mold which is then closed. PA1 (2) A means for fixing the coils in the mold by charging melted resin under pressure exhibits excellent efficiency in terms of mass production but involves the problem that the coils are sometimes deformed by the pressure of the resin used. PA1 (3) Methods for resolving the problem described in (2) include a method in which coils are placed in a mold and resin which is liquid at room temperature is injected into the mold under reduced pressure and then solidified by heating, and a method in which solid resin is placed in mold together with coils and then melted under pressure so as to penetrate between the coils. Such methods, however, involve certain disadvantages since these methods require many molds and much working time and thus lack efficiency in terms of mass production.
The technique disclosed in Japanese Patent Laid-Open No. 125061/1980 also has the following problems:
1. There is a possibility of producing deviations in the shape of coils or damaging the coils during the shaping of the coils that is performed by covering them with a mold.
2. It is very difficult to produce a large number of armatures.
The technique disclosed in Japanese Utility Model Laid-Open No. 75702/1978 also has the problems that coils are easily broken because they are bent in a complicated manner and that resin molding is extremely difficult.
The armature described in Japanese Utility Model Publication No. 31176/1981 must be provided with an insulating sheet to provide insulation between the iron core of a stator and the winding of the armature.
In the armature described in Japanese Patent Laid-Open No. 125061/1980 or an armature formed by pressure injection, portions of the winding of the armature which adhere to the surface of the mold are produced when the heated resin is poured or semi-solidified resin is injected under pressure, and, when the armature is separated from the mold after solidification of the resin, the winding of the armature adhering to the mold is exposed to the air on the sides of the armature and on the end surface opposite to the gate through which the resin is injected. When the thus-formed armature is combined with a core or a case, therefore, the exposed portions of the winding of the armature are in some cases rubbed and produce short circuiting owing to vibrations caused by high-speed rotation during the use of the armature. Projecting edges are produced on the armature during assembly thereof and may sometimes bring about short circuiting upond contacting the core or the case. The above-described armature therefore involves the problems that an insulating member such as an insulating sheet or the like must be provided for the purpose of preventing any short circuiting and that the armature cannot be precisely combined with the core or the case because of the presence of projecting edges or burrs.
A revolving electric device of the type in which a printed board is fixed to one end of an armature and the terminals of the coils of the armature are connected to the printed board, as described above in the prir art, is generally of the type in which the terminals of the armature coils emerge from the end of the armature. In this case, in order to allow soldering of the terminals of the armature coils to the printed board, a hole or notch through which the terminals of the armature coils can be passed must be provided in the printed board, or the terminals of the armature coils must be held between the printed board and the end of the armature and extended to the side of the printed board. A hole or notch must therefore be provided in the printed board and this results in limiting the space available for printed wiring, as well as producing a problem with respect to the strength thereof. In order to remove this problem, the area of the printed board has to be increased, but since an increase in the area of the printed board runs counter to the desire to decrease the size of the armature, no attempt can be made to reduce the size of the latter in the above-described prior art.
In addition, in the above-described prior art, since the end from which the terminals of the armature coils emerge has a flat surface, the terminals of the armature coils are brought into contact with other parts or bent at their roots during work, resulting in a great risk of the breaking of wires. The operator therefore has to use excessive concentration in operating the armature and this greatly strains the nerves.
Furthermore, when the terminals of the armature coils are extended to the side of the printed board, the terminals of the armature coils are bent in a complicated manner or broken between the printed board and the end of the armature, resulting in the possibility of breaking the wires. There is therefore a disadvantage in that the operator's nerves are greatly strained.
The above-described cylindrical armature of the prior art also involves a problem in that the bore of the armature is inclined in one direction from one end to the other and thus shows a great difference in diameter between its two ends. The gap between the rotor and the winding in the stator is thus enlarged, adversely affecting the performance of the armature, particularly rotational torque. There is also a problem in that the armature winding inserted into the mold may be pushed on and adhered to the mold which forms the bore surface of the armature by the resin injected into the mold owing to pressure injection of the molding resin, and the armature may thus be formed with the winding exposed through the molding resin. When such an armature is assembled as a revolving electric device, the exposed portion of the armature winding thereof causes the shape of the armature to be changed to project toward the rotor side owing to vibrations and heat generated during high-speed rotation of the revolving electric device, and thus adversely affects the function of the armature.